The present invention relates to a midsole structure of an athletic shoe, and more particularly, a midsole assembly having a corrugated sheet therein.
A sole for an athletic shoe used in various sports includes a midsole formed of a soft elastic material to secure cushioning properties and an outsole fitted to the bottom surface of the midsole and directly contacting the ground.
Not only cushioning properties but also running stability are required of an athletic shoe. That is, there is a need to prevent over-pronation or over-supination that causes an excessive lateral or transverse deformation of a shoe sole after striking onto the ground.
As shown in Japanese utility model application publication No. 61-6804 and Japanese patent application laying-open publication No. 11-203, Mizuno Corporation proposed a midsole assembly having a corrugated sheet therein to prevent such an excessive lateral or transverse deformation.
In the midsole assembly described in the above-mentioned publications, a corrugated sheet having a wavy corrugation is disposed in a heel portion of a midsole. Therefore, at the time of striking onto the ground, a resistance force occurs to restrain lateral or transverse deformation of the heel portion of the midsole and thus, running stability is achieved.
By inserting a corrugated sheet into a midsole heel portion, the midsole heel portion tends to be less deformed in the lateral or transverse direction and running stability is improved, but especially in the case of using a corrugated sheet formed of a high elastic material, the midsole heel portion becomes less deformed in the vertical direction as well and cushioning properties on landing tend to be decreased.
As shown in Japanese patent application laying-open publication No. 11-346803, Mizuno Corporation proposed a midsole structure in which a plurality of through holes or cushion holes are formed in a midsole having a corrugated sheet therein. In this case, since vertical deformation of the midsole is easy to occur at regions where the cushion holes are formed, the cushioning properties on landing are improved.
However, in this case, when a cushion hole having a greater diameter is used to further improve cushioning properties of the midsole, a midsole portion having a cushion hole formed therein is easy to lose its elasticity and during a prolonged use, cushioning properties of the midsole will be conversely lowered.
An object of the present invention is to provide a midsole structure of an athletic shoe that can prevent loss of elasticity of a midsole at regions where cushion holes are formed and that can improve durability of the midsole at regions having cushion holes formed therein. Another object of the present invention is to enhance flexural rigidity of a midfoot portion and to improve flexibility or bendability of a forefoot portion of an athletic shoe.
A midsole structure of an athletic shoe according to one embodiment of the present invention includes an upper midsole formed of a soft elastic material and extending from a heel region to a forefoot region through a midfoot region, a lower midsole formed of a soft elastic material and disposed at least at the heel region and the forefoot region under the upper midsole, a first corrugated sheet disposed between the upper and lower midsoles, and a second corrugated sheet disposed opposite to the first corrugated sheet between the upper and lower midsoles and having a corrugated surface that forms a laterally extending through hole with the first corrugated sheet.
In this case, since the first and second corrugated sheets are provided between the upper and lower midsoles, the heel region of the shoe is prevented from deforming laterally, thereby securing running stability. Also, since the through hole is formed between the upper and lower midsoles as a cushion hole, the midsole is easy to deform in the vertical direction at regions where the through hole is formed, thereby securing cushioning properties at the time of landing.
Furthermore, in this embodiment, the through hole is formed of corrugated surfaces of the first and second corrugated sheets. That is, in this case, edge portions of an opening and inner circumference of the through hole are reinforced by the corrugated sheets. In other words, through-hole-formed regions of the upper and lower midsoles are reinforced by the corrugated sheets. Thus, even when a shoe with a through hole of a greater diameter is used during a prolonged period, loss of elasticity or permanent set in fatigue of the through-hole-formed regions of the midsole can be prevented and durability of the through-hole-formed regions of the midsole improve. Also, because the diameter of a through hole can be made larger, lightening of the weight of the whole midsole can be promoted.
In another embodiment, since the through hole is formed at the shoe heel region, cushioning properties on landing at the shoe heel region can be improved.
In a still another embodiment, since the through hole is formed at the shoe midfoot region, cushioning properties on landing at the shoe midfoot region can be improved. Also, the through hole has an oblong and elongated shape (in a shoe elongated direction) in cross section, and the corrugated surfaces of the first and second corrugated sheets are provided along the elongated shape of the through hole. Thus, the through hole of such an elongated shape exercises a so-called xe2x80x9cshank effectxe2x80x9d, and flexural rigidity of the shoe midfoot region or shank portion increases. Thereby, flexibility or bendability of the shoe midfoot region decreases and as a result, flexibility or bendability of the shoe forefoot portion can be relatively improved. Moreover, in this case, torsional rigidity of the shoe midfoot portion can be set at a higher value, thereby restraining torsional deformation of the shoe midfoot region during activities.
The through hole may have a generally fusiform cross section. Such a through hole is formed of a concavely curved surface at a crest portion of a wavy corrugation of an upper corrugated sheet and a concavely curved surface at a trough portion of a wavy corrugation of a lower corrugated sheet.
The through hole may have a generally eyebrow-shaped cross section. Such a through hole is formed of a concavely curved surface at a crest portion of a wavy corrugation of an upper corrugated sheet and a convexly curved surface at a crest portion of a wavy corrugation of a lower corrugated sheet. In this case, a radius of curvature of the convexly curved surface at the crest portion of the lower corrugated sheet is greater than a radius of curvature of the concavely curved surface at the crest portion of the upper corrugated sheet. Alternatively, such a through hole is formed of a convexly curved surface at a trough portion of a wavy corrugation of an upper corrugated sheet and a concavely curved surface at a trough portion of a wavy corrugation of a lower corrugated sheet. In this case, a radius of curvature of the convexly curved surface at the trough portion of the upper corrugated sheet is greater than a radius of curvature of the concavely curved surface at the trough portion of the lower corrugated sheet.
The through hole may have a generally oval cross section. In the alternative, the through hole may have a concavely curved surface at the crest portion of a wavy corrugation of a first (or a second) corrugated sheet on the side of the upper midsole.
In these cases, when an upper surface of the through hole is formed of a concavely curved surface of a crest portion of an upper corrugated sheet, flexural rigidity of the shoe midfoot region can be remarkably increased. This results because the concavely curved surface is bent in a direction opposite the bending direction of the shoe midsole region when a force is applied to the shoe so as to bend the shoe midsole region upwardly. In such a manner, flexibility or bendability of the shoe midfoot region can be remarkably decreased, and as a result, flexibility or bendability of the shoe forefoot region can be further improved.
In a further embodiment, a first corrugated sheet extends from the heel portion to the forefoot portion on the side of the lower midsole and a second corrugated sheet extends from the heel portion to the midfoot portion on the side of the upper midsole and through holes are formed at the shoe heel and midfoot regions.
In this case, since the first corrugated sheet extends to the forefoot portion of the upper midsole, the shoe forefoot region is easy to bend along a crest or trough portion of a wavy corrugation of the first corrugated sheet, thereby further improving flexibility or bendability of the shoe forefoot region.
In a still further embodiment, a through hole formed at the shoe midfoot region has an oblong and elongated shape in cross section and corrugated surfaces of a first and second corrugated sheet are provided along the elongated shape of the through hole. Thus, the through hole of such an elongated shape develops a so-called xe2x80x9cshank effectxe2x80x9d, and flexural rigidity of the shoe midfoot region or shank portion increases. Thereby, flexibility or bendability of the shoe midfoot region decreases and as a result, flexibility or bendability of the shoe forefoot portion can be relatively improved. Moreover, in this case, torsional rigidity of the shoe midfoot portion can be set at a higher value, thereby restraining torsional deformation of the shoe midfoot region during activities.
The shoe forefoot portion may also have a through hole, which improves cushioning properties of the shoe forefoot portion.
In an additional embodiment, a first or second corrugated sheet has a pair of flange portions extending upwardly and/or downwardly on both edges of a medial side and a lateral side. In this case, since the flange portions are disposed at opposite ends of the upper and/or lower midsole, lateral or transverse deformation of the midsole can be restrained by the flange portions. Thereby, running stability of the shoe is further increased.